1. Field of the Invention
This invention relates to furnaces and in particular to high efficiency furnaces, such as for domestic use.
2. Description of the Background Art
In one form of domestic furnace utilizing a gaseous hydrocarbon fuel, a series of parallel heat exchanger cells are provided which are fired directly by and receive the combustion products directly from the fuel burner. Conventionally, the heat exchanger cells are arranged in a side-by-side, vertical array. The combustion products are delivered from the cells to a superjacent flue collector box and the collector box passes the combustion products to the chimney, stack or flue gas outlet.
It is further conventional to provide increased efficiency in such a domestic furnace by providing air moving means for providing a forced flow of the combustion products. To provide improved efficiency in such furnaces, it has further been conventional to provide a secondary heat exchanger receiving the combustion products from the flue collector box so as to be in further heat transfer association with the air being heated. The secondary heat exchanger removes additional heat from the combustion products before they are delivered to the stack, thereby increasing the overall efficiency of the furnace.
One example of such a forced-air furnace is illustrated in U.S. Pat. No. 4,261,326 of Harry Ihlenfield. As shown therein, a furnace includes a secondary heat exchanger, or recuperator cell. As indicated therein, the use of the secondary heat exchanger reduces the temperature of the combustion products leaving the furnace to less than approximately 200.degree. F., whereas the temperature of the exiting combustion products in a conventional, single heat exchanger furnace may be 450.degree. F., or more. The resultant increase of efficiency can be 10% or more. Thus, while in a conventional single heat exchanger furnace, an efficiency of approximately 75% can be realized in furnaces utilizing such secondary heat exchangers, an efficiency of 90% or more may be obtained.
A problem, however, arises in the operation of such high efficiency furnaces in that the low temperature of the exiting flue gases causes the formation of liquid condensate from the products of combustion, and it is possible in domestic secondary heat exchanger furnaces to generate up to a gallon of condensate per hour of operation.
Additionally, the sulfur content of the combustion products resulting from the combustion of natural gas is, in many instances, sufficient to produce undesirable quantities of sulfur-dioxide and sulfur-trioxide. Oxides of nitrogen can also be produced from the combustion of natural gas. Some of these oxides tend to dissolve in the condensed water, forming an acidic solution which presents a disposition problem. If this acidic solution condensate is permitted to remain within the components of the furnace or to return back to the furnace components from the outlet flue, serious corrosion problems can arise, shortening the useful life of the furnace components and presenting undesirably high maintenance requirements.
A number of attempts have been made in the prior art to remove the acidic condensate from the furnace components as they are produced. One attempted method to solve this problem is shown in U.S. Pat. No. 4,164,210 of George T. Hollowell, wherein a condensate drain is provided at the foremost portion of the secondary heat exchanger.
A condensate separator is provided in U.S. Pat. No. 4,289,730 of Ronald S. Tomlinson, which patent is owned by the assignee hereof. As shown therein, the condensate separator is disposed to receive the condensate from the secondary heat exchanger prior to the delivery of the combustion products to the blower, which, in turn, delivers the combustion products to the discharge flue. In the Tomlinson patent, the separator further includes neutralizing material for neutralizing the acidic component of the condensate prior to the discharge thereof as to the conventional household drain. In the Tomlinson patent, the improved condensate separator and neutralizer is further arranged to be self-flushing.
In the furnace of the Ihlenfield U.S. Pat. No. 4,261,326 discussed above, the drain is similarly connected to the foremost portion of the secondary heat exchanger so as to remove the condensate prior to the delivery of the combustion products to the blower.
Thus, it has been conventional in the prior art to utilize means for removing the condensate from the combustion products before they enter the blower.